C106 Colorimetric Determination of Concentration Pre-Lab Write your answers to t

Question

C106 Colorimetric Determination of Concentration Pre-Lab Write your answers to these in a new Word document. Include a heading with your name, date, and section number at the top of the page. Number your answers with the corresponding question number. Save your document as a PDF and upload to Blackboard in the Pre-lab assignment area for this experiment 1. Explain how the concentration of a colored solution can be determined by shining a beam of light through it (in evaluating your answer, we're looking to see that you have a reasonable grasp of the overall theory of this experiment) The colorimeters you willise in this experiment are capable of measuring the absorbance of a solution at four different wavelengths of light. Explain how you will determine which wavelength you will set yours to before you measure the absorbances of your solutions. Your experiment will require you to make four standard solutions, each to a different concentration of Allura Red AC. Describe how you will make these. 3. Refer to the Beer's Law Plot in the Background. What absorbance would a solution with a concentration of 0.0037 M have? What concentration would a solution with an absorbance of 0.25 have? 4. You are instructed to deliver"7mL" of liquid from a burette. How many ml can you actually dispense and to what decimal place should you take your burette readings? (If you have no idea, see the document "Lab Techniques" on the course webpage.)

Explanation / Answer

1) Absorbance is the important factor in determining concentration of colored solution in the colorimetric analysis. As colorimeter works only on one wavelength and only in visisble region. IN the colored solution, the intensity of color of solution is the absorbance of solution. When beam of light is added then the colored solution absorb the light and it will emit transmittance which gives the concentration of solution.

2) As we know Allura Red AC is red in color. Generally, observed color is complimentry to the color of light absorbed. Red is complimentry to green. So the light absorbed is green in color of wavelength 470 nm. Wavelength of 640-700 nm are not absorbed but transmitted, and give perception of red color.

3) Firstly we have to prepare stock solution of molarity 1.97 X 10-4 M in available standard volumetric flask. Then take four volumetric flask of 100 ml. From the stock solution of Allura Red AC take 5 ml, 10 ml, 15 ml and 20 ml and add in the 100 ml volumetric flask and then make upto 100 ml. These are standard solution of Allura Red AC.

5) If we are instucted to deliver 7 ml of liquid from the burette, then error of +-0.02 ml is possible. So it can possible we will deliver 7.02 or 6.98 ml from the burette.

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